Numerical study on the mechanism of spontaneous ignition of high-pressure hydrogen during its sudden release into a tube

Abstract

Hydrogen is regarded as the promising energy carrier in the 21st century and high-pressure storage is selected as the best option. However, spontaneous ignition would be induced if high-pressure hydrogen is suddenly released. Three cases were numerically conducted to gain an insight into the mechanism of the spontaneous ignition and to validate against our previous experimental results. Result show that a hemispherical shock wave is first produced. Then it is reflected as reflected shock wave after hitting the tube wall and interacts with other reflected shock waves to form the Mach disk, shock triple point and a barrel shock. The height of the Mach disk gradually decreases and finally it disappears. Meanwhile, the shape of hydrogen jet changes from a forward convex shape to a backward concave shape and hydrogen/air mixture layer is formed near the tube wall and the center of the tube. The temperature of the shock-affected region gradually increases and its area thickens. After maintenance of high temperature for a period of time, spontaneous ignition firstly occurs at the tube boundary. Present numerical results not only reproduce the ignition conditions but also the ignition positions indicating that the model is an effective tool for hydrogen safety engineering.